The present invention relates to a display device, and more particularly, to an active-matrix type liquid crystal display device, in which a liquid crystal display driving circuit is formed on the liquid-crystal-side surface of one of two substrates that are arranged to face each other with liquid crystal being disposed therebetween.
In an active-matrix type display device, pixel regions are defined on a liquid-crystal-side surface of one of two transparent substrates that are arranged to face each other with liquid crystal being disposed therebetween, wherein the pixel regions are surrounded by gate signal lines, which extend in the x direction and are arranged in parallel in the y direction, and drain signal lines, which extend in the y direction and are arranged in parallel in the x direction.
Each pixel region is provided with a thin film transistor which is driven by scanning signals from a gate signal line, on the one hand, and a pixel electrode to which video signals are supplied from a drain signal line, on the other hand, through that thin film transistor. An electric field is generated between the pixel electrode and a counter electrode which is formed opposite it on the liquid-crystal-side surface of the other transparent substrate with an intensity which corresponds to the applied video signal, so as to control the light transmittivity of the liquid crystal.
Further, there is a known liquid crystal display device having the above constitution, which also comprises a scanning signal driving circuit and a video signal driving circuit for respectively supplying signals to respective gate signal lines and respective drain signal lines on the other transparent substrate on the side facing the liquid crystals. Each circuit is comprised of a large number of MIS (Metal-Insulator-Semiconductors) type transistors having a constitution similar to that of the thin film transistors in the pixel regions. These circuits can be formed simultaneously with the formation of the pixels. In this case, polycrystalline silicon (Poly-Si) has been used as semiconductor layers of the thin film transistors and the MIS type transistors.
However, with respect to a display device having the above-described constitution, when the liquid crystal display device is used as a display device of a portable telephone, there is the problem that the power consumption is relatively large.
Further, since a video signal driving circuit uses a dynamic memory, is the problem that a leakage current flows into the thin film transistor which constitutes the dynamic memory.
Further, it has been also pointed out that when the dynamic memory generates photons in a semiconductor layer due to light from the outside, this generation of the photons gives rise to a more adverse influence than the thin film transistor formed inside of the pixel region, for example.